A nature guide illustrated by insights

Another Life: May's memorable rains fell in fat, juicy, slightly sinister drops that spoke of water sucked up from a warming ocean and condensed in the chilly spring air. For hours and days on end, the islands vanished behind slow-moving palls of slatey grey. No water problems there, one could think.

Yet for one set of islands - Aran, in Galway Bay - hanging on to the rain has always been a challenge.

As slabs of fissured limestone, the islands lose their rainfall rapidly through cracks in the surface rock. Only far underground beneath the bare terraces is it trapped by layers of ancient, fossil soils, or shales, left by changes in sea level over time. Without these "clay wayboards", the island's wells would run dry, and flushing the loos for 200,000 summer tourists would become impossible.

Such insights have been shared "as Gaeilge" by Con O'Rourke, a past president of the Institute of Biology Ireland, with countless trainee teachers, and with tourists on his natural history courses. Now, they illumine his Nature Guide to the Aran Islands (Lilliput Press, €15), a splendidly-illustrated handbook. The islands have seen long periods when they were "in a perpetual state of being investigated", as Tim Robinson has put it, but this is the first popular guide to the flora, fauna and geology of one of Ireland's more marvellous ecosystems.

The three islands are so obviously fragments of the same rock which makes up the Burren that one expects to find them repeating much of the mainland experience. But away from the dramatic cliffs and storm beaches there is scarcely one stone on another that has not been placed by human hands, and hardly a cupful of arable soil that has not been stirred - in places, directly manufactured - by human hands.

In the Burren uplands there is often a sense of wilderness, of a great historic distance between the landscape and its early farmers. On the islands, the intimate coexistence of people, rock and wild plants has been as current and tangible as the nearest stone wall. But the modern change in farming brings sharp ironies: the Rural Environment Protection Scheme (Reps) "has," says Dr O'Rourke, "undoubtedly improved the visual aspects of Aran farming". The old wrecked equipment and vehicles have been cleared away, and Reps rewards maintenance of the islands' 2,400km of magnificent walls around thousands of fields. But the vegetable gardens, so painfully created with seaweed and sand, are disappearing, as cash takes over the last shreds of self-sufficiency.

One of Con O'Rourke's photographs is emblematic: a dozen farmers on a Reps course on Inis Meáin are grouped in a field, stooping over something in the grass. They are "identifying purple milk-vetch, a protected species". It is, indeed, precious, being found in Ireland only on Inis Meáin and Inis Mór. The islands have also preserved cornflowers and darnel, once thought extinct in Ireland as weeds of traditional cereal tillage.

Many of the 437 plants recorded so far on Aran have figured in herbal remedies, and this gave the islanders a special knowledge of plants and respect for their value. The pink-starred herb robert, for example, particularly abundant in Aran, was well-known as a treatment for kidney disease and of "red water" in cattle. Chewing dillisk, the red seaweed, was a remedy for children's intestinal worms, and it was even exported to mainland towns as a hangover cure. In the switch to conventional medicine, such knowledge has melted away.

If the fields are ever abandoned, says Dr O'Rourke, Aran's Burren-type flora will disappear under hazel scrub, as is already happening in parts of Co Clare. Already, a reduction of grazing in the pastures of Inis Mór has been linked to a fall in the population of choughs, the islands' most distinctive land birds.

Farmers have to be rewarded to look after their unique natural environment, but "subsidising them to persist with old-fashioned husbandry runs the risk of turning the islands into a folk park". In finding the balance, some of the rewards of ecotourism must go the farmers' way.

The pressure of tourism on the natural fabric of Aran is not entirely new. Even in 1892, improved ferry services brought Sunday trippers from Galway to loot the limestone grykes of their exquisite maidenhair ferns.

Today's hordes pose "an even greater threat to the plant's survival", says Dr O'Rourke, but books like his can make respectful ecotourists of anyone willing to learn. Islands - including Ireland itself - set particular puzzles in natural history: how did everything arrive, and why some things and not others?

The small ones also offer simple ecosystems in which to study ecology. Cape Clear, off west Cork, has already become a focus for learning about birds and whales. A course called "The Ecological History of Ireland" will be held there from July 3rd-7th, organised by Dr Geoff Oliver and Dr Paddy Sleeman.

Details from www.oilean-chleire.ie